Medical syringes are available in a large variety of sizes and configurations for delivering liquids or gases to a patient. Syringes are usually equipped with either a nozzle tip or a hypodermic needle for administering medications. Many different lengths, diameters, and styles of nozzle tips and needles are used on syringes. Syringes may also be available in a variety different volume sizes. Available volume sizes may range from about 0.3 mL to 60 mL, which is typically sufficient to cover the wide range of dosages required for most injections. Some syringes may also be equipped with safety features for reducing the incidence of accidental needle sticks.
There is often a problem with many conventional syringes in obtaining an accurate dosage measurement of small amounts of medicine. When low dosages of medication are prescribed, it can sometimes be difficult for the health care professional or the individual administering an injection to precisely measure the amount of fluid or gas to be injected. In some cases, for example, the gradations or markings of many low-dosage syringes such as 0.3 mL syringes are simply too close together for an accurate measurement to be made. On a 0.3 mL syringe, for example, there is often an insufficient amount of room for placement of the extremely small gradations. Some 0.3 mL syringes may have a maximum of 60 gradations on the syringe barrel, amounting to one gradation mark for each 0.005 mL (5 microliters). Some micro dosages are prescribed in increments lower than 0.0025 mL (2.5 microliters), however. Thus, the scale on those 0.3 mL syringes having 60 gradation marks still cannot measure many micro dosages of medication without interpolation.
Syringes are sometimes used in ocular procedures such as cataract extraction or intraocular lens (IOL) implantation for delivering a small amount of liquid (e.g. sodium hyaluronate) to the patient's eye during surgery. In some cases, injections are made to the human eye with dosage quantities of less than 0.005 mL (5 microliters), which is typically the smallest gradation available on a 0.3 mL syringe. As a result, accurate dosage is sometimes difficult and susceptible to error using 0.3 mL syringes, which often have measurement gradations that do not permit measurement in 0.005 mL or smaller increments.
Many medications given in low dosages can be considerably expensive. In the treatment of certain ocular diseases such as age related macular degeneration (ARMD), for example, a very small, less than 0.05 ml dosage of the pharmaceutical Lucentis® injected into the eyes of a patient may cost in excess of $1.000. Due to the high expense associated with such drugs, small dosage errors in the measurement of these drugs can result in significant expense.
Another growing area of low dosage injections is with small animals. The treatment of diabetes in cats, for example, frequently requires insulin injections of dosages less than 0.05 mL, and sometimes in increments as low as 0.005 mL. Dosages this minute are extremely difficult to read, even using a 0.3 mL syringe with 60 gradation lines. If a person caring for their pet at home misreads the gradations markings on the syringe, an inaccurate amount of medication may be injected into the animal.
One method used to minimize this measurement issue with pets is the increasing use of U-40 insulin, which is designed specifically for use with small animals such as dogs and cats. Traditionally, small diabetic pets were injected with U-100 insulin which is the same insulin used by humans. Now some veterinarians are prescribing U-40 insulin which is diluted to 40% the strength of U-100 insulin. By being diluted, more of the syringe can be filled with U-40 insulin, thus making it easier for the pet owner to accurately dose extremely small amounts of insulin. Because U-40 insulin costs significantly more than U-100 insulin, however, many small pet owners continue to use the more concentrated and difficult to administer U-100 insulin.
Often, the dilution of certain types of medicines is not a practical solution to reducing dosage errors. For some medications, for example, the medicine may not be compatible with dilution. Individuals administering such medications will continue to have to deal with the risk of measurement errors until a better solution is discovered.
Accordingly, there is a continuing need for new and alternative syringes that can be used to accurately deliver small dosages of fluids.